This is an application for a career development award to provide the PI with training in integrative biosciences and biomedical engineering in preparation for a career as an independent investigator focused on the impact of inflammopathies (e.g. sepsis) on subcellular energetics. Sepsis leads to ATP depletion and cytochrome aa3 (terminal component of the electron transport chain) reduction. The PI will investigate the impact of uncontrolled sepsis (rat cecal ligation and puncture) and established sepsis therapies on cytochrome aa3 oxidation state (Cytox), tissue pO2, ATP:ADP ratio, and survival in order to better understand the impact of this observed energetic quiescence (SA1). I hypothesize that this quiescence is adaptive and that inability to shut down metabolism will be associated with morbidity. The role of tissue O2 in inflammation is not clear. O2 can be both helpful (allowing for aerobic respiration) and harmful (reactive oxygen species [ROS] production). The PI will alter tissue O2 with/without selective cytochrome aa3 inhibition in septic rats while measuring tissue pO2, Cytox, markers of oxidative stress, ATP:ADP ratios, hypoxia-induced factor 1(HIF-1) expression, and survival to determine if tissue O2 is protective during inflammation, as well as elucidate the underlying mechanism(s) for its impact (SA2). I hypothesize sepsis-induced quiescence diminishes the impact of low tissue pO2, and that supranormal tissue pO2 leads to ROS production and morbidity. Preconditioning (PC) provides cellular protection in a variety of pathologies. While pharmacologic PC is protective in sepsis, it is clinically impractical, thus the PI will test the efficacy of hypoxic and ischemic PC as a protective mechanism. After a brief period of controlled hypoxia or remote ischemic preconditioning (RIPC), sepsis will be induced in rats. Cytox, expression of HIF-1, heme-oxygenase-1 (HO-1), inducible nitric oxide synthetase, and survival will be measured (SA3). I hypothesize that RIPC will lead HIF-1 upregulation, attenuating ROS production. Demonstration of efficacy would suggest a practical means of pre-empting sepsis in high-risk patients. HIF-1 attenuates ROS production and induces mitochondrial biogenesis (via HO-1) which are likely prosurvival for the organism but may limit T cell efficacy (ROS are bactericidal). The impact of HIF-1 downregulation on the balance of cellular energetics and immunocompetence is not clear. The PI will compare sepsis tolerance in wild-type and knockdown mice deficient in the HIF-1 I.1 isoform, specifically looking at HIF-1 expression, Cytox, oxidative stress, and survival (SA4). While HIF-1 suppression in lymphocytes improves survival in sepsis (by increasing antibactericidal activity), I hypothesize that global HIF-1 downregulation will increase mortality due to overproduction of harmful ROS. Completion of these Specific Aims will increase our understanding of the impact of sepsis on cytochrome aa3 oxidation state, subcellular energetics, and HIF-1, ultimately providing a foundation for additional work to develop novel therapeutic strategies for this devastating disease process.